The present invention relates to apparatus and methods for active control of dynamic pressure oscillations in a gas turbine combustion system. More particularly, the invention relates to using active feedback and control drivers to reduce combustion dynamics in an industrial gas turbine combustion system with single or multiple chambers which are linked to each other through their fuel systems and common air supply.
High dynamics can limit hardware life and/or system operability. Thus, there have been various attempts to control combustion dynamics, to prevent degradation of system performance. There are two basic methods for controlling combustion dynamics in an industrial gas turbine combustion system: passive control and active control. As the name suggests, passive control refers to a system that incorporates certain design features and characteristics to reduce dynamic pressure oscillations. Active control, on the other hand, incorporates a sensor to detect, e.g., pressure fluctuations and to provide a feedback signal which, when suitably processed by a controller, provides an input signal to a control device. The control device in turn operates to reduce the dynamic pressure oscillations.
An effective method for passive control of pressure oscillations in industrial gas turbine combustors is disclosed in U.S. Pat. No. 5,211,004, the entire disclosure of which is incorporated herein by this reference. The '004 patent describes a fuel supply system having a fuel passage with an upstream orifice, a downstream discharge orifice and a captured response volume defined between the orifices. The upstream orifice has a high-pressure drop for performing the function of isolating the fuel system from the premix zone and providing uniform fuel distribution. Moreover, the upstream orifice provides a pressure drop such that in the pressure in the captured response volume approximates the pressure of the compressor discharge air. The downstream orifice provides a low pressure drop from the captured response volume to the combustor. The level of the downstream pressure drop is selected so that the fuel system has a specific phase response as compared to that of the air system. This two-stage nozzle has been very effective in reducing combustion dynamics related to the fluctuation of fuel/air ratio concentration by matching fuel system and air system responses to pressure fluctuations.
There have also been developments in the area of active control. See, e.g., Annaswamy et al., "Active Control in Combustion Systems," IEEE Control Systems, December, 1995, pp 45-63, which is incorporated herein by this reference. As previously mentioned, active control requires that a sensor be provided to supply feedback, a controller to process the feedback signal into a control signal and a control device responsive to the control signal. On laboratory scale combustion test rigs, such systems have been generally effective in controlling dynamic pressure oscillations by applying a control device to either the air system or the fuel system of the combustor. Typically, the pressure control device, such as a loud speaker, has been applied for control of the air system while a flow control device, such as a valve, has been applied for control of the fuel system. Most of the work has focused on controlling a single laboratory scale reaction zone.
However, even with a laboratory scale reaction zone, there have been issues with both the frequency response and power consumption of the control device. Usually, power consumption is a problem for the air system control whereas frequency response is the issue for fuel system control. As will be appreciated, for an industrial scale gas turbine (30-250 mW) the air and fuel flows are orders of magnitude larger. Thus, these issues have severely limited the applicability of active control schemes. To the inventors knowledge there has not been a successful application of such an active control scheme to an industrial gas turbine.